This invention relates to the process of super activating the negative iron electrode of an iron-nickel or iron-air battery. More particularly, this invention relates to the reaction of sulfur substituted organic acids of the thiolic, dithiolic, dithionic or mercaptocarboxylic types with iron active battery materials to provide activated battery plates.
Certain parameters are fixed in battery cell design, such as grams of iron oxide that can be loaded per cubic centimeter of electrode volume. Therefore, any means of increasing the actual utilization of iron oxide would be highly desirable. Another serious problem in sealed battery cells employing alkaline iron electrodes, has been the vigorous evolution of hydrogen gas during most of the charging process.
The iron battery electrode plate is composed of a finely divided iron powder, deposited or impregnated in a supporting plaque and compacted to a desired density. When pure iron oxide powder is used as an electrode active material in an alkali electrolyte, a battery has limited utilization due to the rapid formation of a passivating film on the iron surface.
To facilitate the discharging of the electrode plate, a reaction promoting additive for the electrode active material is needed. Such an additive should have the ability to activate the entire substance, though present in relatively small amounts.
The addition of ferrous sulfides or elemental sulfur as additives to iron oxide powder in a negative iron electrode is known in the art, as shown in U.S. Pat. No. 2,871,281 to Moulton and U.S. Pat. No. 3,507,696 to Jackovitz. These methods have involved sulfide absorption by the iron electrode from a solution of hydrogen sulfide gas in the electrolyte or mechanical mixing of ferrous sulfide with iron oxide and fusion of elemental sulfur with iron oxide at elevated temperatures.
Our invention relates to a total process which is a less expensive and simpler means for activation of the iron oxide powder. Electrodes activated by our method show an increase in the rate of charge acceptance without appreciable gassing, and their performance can be favorably compared with electrodes activated by the molten sulfur technique, which usually yields outputs in the range of 0.50 to 0.55 amp.-hr/gram of active material.
The reaction of iron oxides with mercaptocarboxylic acids in our method, generally produces a mixture that contains a chelate that is stable against hydrolysis and extremely useful as battery active material. Metal salts of succinic and succinamic acids have been disclosed as detergents and rust inhibitors in U.S. Pat. No. 3,271,310 to Le Suer and U.S. Pat. No. 3,365,477 to Gee, but neither disclose mercapto-succinic acid salts of metals, which are corrosion producers.